Kim Antes, age 10, of Windsor, Pennsylvania, for her question:

How lone does it take an oyster to make a pearl?

There are, as you know, large pearls and small pearls. As a rule, the difference depends upon the time it takes the oyster to make them. His juicy soft body is very sensitive to scratches and he lines the inside walls of his shells with a smooth glossy nacre. This lovely material glows like pale, multicolored moonbeams. Nacre is called mother of pearl and the oyster spends his whole life adding thin thin layers to the inside of his shell. Sometimes a gritty grain of sand or maybe a scratchy little worm gets between the shell and his soft body.

The oyster solves this problem by covering the scratchy morsel with nacre    every time he recoats his walls. In about two or three years, the layers and layers of nacre build a tiny pearl. After seven years or so, the pearl may be as big as a pea. This is a natural pearl, worth hundreds of dollars. When a grain of grit is placed inside an oyster, he can be coaxed to create a cultured pearl. This is done when he is three years old and the pearl is big enough to join a necklace after about four years.